1. Field of the Invention
The invention relates to electrical filter circuits utilizing charge transfer devices comprising individual charge transfer device elements wherein four-terminal quadripole resonators which are designed as self-contained closed looped circuits and which determine the frequency dependent transmission characteristics of the filter circuits and wherein successive four-terminal resonators are interconnected by way of coupling circuits.
2. Description of the Prior Art
Filter circuits of the CTD type are known as, for example, as described in German LP 2,453,669. Other specific embodiments of such circuits are described in German AS 2,534,319 as well as in German AS 2,608,582. In these publications, it is also described how bucket brigade devices and bucket brigade circuits as well as charged coupled devices are understood as to be designated as CTD lines. See also the article entitled "Charge-Coupled Devices" appearing in Wireless World of February 1975 pages 61 through 65 describe signal processing with charge coupled devices.
Charge coupled devices are circuits which operate according to the principle of coupled charges. It is for the two types of circuits, BBD and CCD the designation of "CTD installation", (charge transfer devices) has been adapted in the technical vocabulary and this term also characterizes transmission devices that have unidirectional transmission behaviour. CTD devices consist of an integral number as, for example, n individual CTD elements which can be constructed as integrated overall arrangements. Known CTD arrangements must be operated with clock pulse signals having a specific clock pulse frequency f.sub.T and the clock pulse signal is supplied to the individual charge transfer capacitors of the BBD arrangements or to the transfer capacitances of the CCD lines. In practice, generally multiphase CTD arrangements are preferred wherein the clock pulse signals are phased displaced relative to each other such that adjacent transfer capacitances are operated with phase displaced clock pulses. Consequently, if one utilizes a so-called p-phase clock pulse system (p=2, 3, 4 . . . ), then one CTD element consists of p adjacent transfer capacitances. Other technical discussion on these devices is given in the book entitled "Charged Transfer Devices" Academic Press, Inc. New York, San Francisco, London published in 1975.
Filter circuits according to German LP 2,453,669 and German AS 2,534,319, and German AS 2,608,582 utilize as the resonant determining devices self-contained closed looped circuits which are designated in this specification as four-terminal resonators. In German AS 2,534,319 input and output coupling circuits are also illustrated which are designed in the form of lattice filter sections whereby the properties of the CTD arrangements must be considered for the circuit construction. In the case of input and output coupling circuits illustrated in German AS 2,608,582, the .pi. section arrangement is utilized.